I don't know. My phone's usually good for an hour of play on battery alone. For the longer quests like Archon Quests I usually break it up into separate hourlong sessions. And in the worst cases for example in more recent quests there are sections that go on continuously for over an hour, I'll have it plugged in while I play but this will heat up the device a little more than on battery.

It could be your device is too old or isn't up to specs. I use a Xiaomi Mi MIX 3 which usually overperforms against its contemporaries.